1. Field of the Invention
The present invention relates to assays for determining and/or detecting hormones in mammalian body fluids and in particular to assays for determining and/or detecting the luteinizing hormone surge which results in rupture of the preovulatory follicle and release of the ovum at ovulation. More particularly, the invention relates to the use of total gonadotropal alpha peptide chain content in urine as an enhanced indicator of luteinizing hormone content. Even more particularly, the invention relates to an immunoassay suitable for testing for constituents in human urine to determine the human fertile period, that is, the period in which viable sperm and a viable ovum may be present simultaneously in the female reproductive tract.
2. The Prior Art Background
For a number of reasons it may be clinically and/or diagnostically desirable to determine the presence and/or concentration of constituents in mammalian body fluids such as blood serum or urine. In some instances, mammalian hormonal activity and/or metabolism create situations where surges in concentrations of hormones or metabolites in body fluids may be chronologically related to other events. In particular, a surge in the concentration of luteinizing hormones (LH) in human urine may be used to ascertain the fertile period of the menstrual cycle. For couples experiencing difficulty in conceiving there is a need for identifying the optimum period for intercourse or artificial insemination.
The human menstrual cycle is governed by the cyclical release of hormones from the female glands and organs. Such release is predictable and specifically related to ovulation by which ova are released from the ovaries and the lining of the uterus is made ready for pregnancy. Eventually, the released hormones and/or metabolites thereof find their way into the urine. The specific biological phenomena are described in detail in a published dissertation of Kevin J. Catt and John G. Pierce entitled "Gonadotropic Hormones of the Adenohypophysis", which appears as Chapter 3 (pp 75-114) of a treatise of Yen, S. S. C. and Jaffee, R. B., REPRODUCTIVE ENDOCRINOLOGY, 2d ed., W. B. Saunders, Philadelphia (1978). And suffice it to say, that during a normal menstrual cycle, the level of LH in female serum surges to cause the preovulatory follicle to rupture and release the ovum. This process is known as ovulation. The LH surge may be detected in female urine approximately 8 to 24 hours after the surge occurs in the blood. The surge of LH in human urine has thus been used as an indication that the fertile period is ongoing or about to occur and a number of commercial assays for detecting the fertile period have been based on the measurement of LH concentrations in human urine.
Gonadotropins such as LH, follicle-stimulating hormone (FSH), human chorionic gonadotropin (hCG) and thyroid-stimulating hormone (TSH) are all well known hormones as discussed in the Catt et al. dissertation identified above. These hormones are all formed from two peptide chains (an alpha chain and a beta chain) which are non-covalently joined to present the intact hormone. The chains are capable of existing separately; however, they must be joined together to create a biologically active hormone. The alpha chains of LH, FSH, hCG and TSH are essentially identical but the beta chains are all different.
As is known in the art, the intact (holo) hormones and the free alpha and beta chains may be distinguished and assayed separately using various combinations of antibodies to private, public and/or conformational epitopes. In this regard, a public epitope is one that is accessible without regard to whether the chain is free or combined, a private epitope is one that is accessible only on free chains and a conformational epitope is one that is not available on either chain alone but only on an intact hormone. And, as indicated above, commercial fertile period assays have previously been configured to determine the LH surge by assaying for the intact hormone.
It has also been recognized that LH assays could potentially be directed to either total or free LH beta chain. However, there has been no suggestion in the prior art that there might be a sufficient correlation between preovulatory total alpha chain content and intact LH surges in urine to base a fertile period assay on total alpha chain. Even more so there has been no suggestion in the prior art that total alpha chain not only surges contemporaneously with LH but surges to a much greater level so that the assay is much more sensitive and precise.